Drive shaft assembly

Abstract

A two piece type drive (propeller) shaft assembly comprises first and second shafts and a middle elastic member which resiliently connects the first and second shafts end to end so that power can be transmitted. At least one weight is fixed to each shaft at a predetermined unbalance position to shift a principal axis of inertia of the shaft to a desired orientation to suppress whirling motion of the shaft. In each shaft, the at least one weight is located at such a position that the distance of the unbalancing at least one weight from the connected end of the shaft is substantially equal to one third of length of the shaft.

What is claimed is: 
     
       1. A drive shaft assembly comprising first and second shafts each of which has first and second ends; a connecting means for resiliently connecting said first ends of said first and second shafts with each other so that power can be transmitted from one of said first and second shaft to the other;   a first unbalancing means fixed to said first shaft, said first unbalancing means being located at a first unbalance position of said first shaft, said first unbalance position being radially spaced from a center axis of said first shaft, said first unbalance position being separated from said first end of said first shaft by a distance which is substantially equal to one third of the length of said first shaft; and   a second unbalancing means fixed to said second shaft, said second unbalancing means being located at a second unbalance position of said second shaft, said second unbalance position being radially spaced from a center axis of said second shaft, said second unbalance position being separated from said first end of said second shaft by a distance which is substantially equal to one third of the length of said second shaft,   wherein said first unbalancing means is fixed to said first shaft so as to make a principal axis of inertia of said first shaft approximate an inclined straight line which intersects said center axis of said first shaft at said second end of said first shaft and which is apart from said center axis of said first shaft at said first end of said first shaft, and said second unbalancing means is fixed to said second shaft so as to make a principal axis of inertia of said second shaft approximate an inclined straight line which intersects said center axis of said second shaft at said second end of said second shaft and which is apart from said center axis of said second shaft at said first end of said second shaft.   
     
     
       2. A drive shaft assembly according to claim 1 wherein each of said first and second unbalancing means has a predetermined mass, and is used solely because of the predetermined mass, said first unbalancing means being positioned so that a center of mass of said first unbalancing means is distant from said center axis of said first shaft, and said second unbalancing means being positioned so that a center of mass of said second unbalancing means is distant from said center axis of said second shaft. 
     
     
       3. A drive shaft assembly according to claim 2 wherein said first unbalancing means is fixed to said first shaft so that said center of mass of said first unbalancing means is located at said first unbalance position, and said second unbalancing means is fixed to said second shaft so that said center of mass of said second unbalancing means is located at said second unbalance position. 
     
     
       4. A drive shaft assembly according to claim 3 wherein said connecting means comprises an elastic member which resiliently connects said first and second shafts end to end so that power can be transmitted through said elastic member from one of said first and second shafts to the other shaft. 
     
     
       5. A drive shaft assembly according to claim 3 wherein said first unbalancing means is placed in a first imaginary plane which is substantially perpendicular to said center axis of said first shaft and which is separated from said first end of said firstshaft by a distance which is substantially equal to one third of a length of said first shaft, and said second unbalancing means is placed in a second imaginary plane which is substantially perpendicular to said center axis of said second shaft and which is separated from said first end of said second shaft by a distance which is substantially equal to one third of a length of said second shaft. 
     
     
       6. A drive shaft assembly according to claim 5 wherein said first unbalancing means comprises first and second mass members separated from each other, and said second unbalancing means comprises third and fourth mass members separated from each other, said first and second mass members are located, respectively, on two imaginary straight lines which lie in said first imaginary plane and which intersect each other substantially at right angles at a point lying on said center axis of said first shaft, and said third and fourth mass members are located, respectively, on two imaginary straight lines which lie in said second imaginary plane and which intersect each other substantially at right angles at a point lying on said center axis of said second shaft. 
     
     
       7. A drive shaft assembly according to claim 6 wherein said first and second mass members are fixed to an outside circumferential surface of said first shaft, and said third and fourth mass members are fixed to an outside circumferential surface of said second shaft. 
     
     
       8. A drive shaft assembly according to claim 7 wherein said connecting means comprises an elastic member which has a tubular shape, one of said first and second shafts being fit in said elastic member and the other of said first and second shafts being fit over said elastic member. 
     
     
       9. A drive shaft assembly according to claim 5 wherein said first and second unbalancing means are positioned so that a centrifugal force acting on said first unbalancing means and a centrifugal force acting on said second unbalancing means have opposite directions. 
     
     
       10. A drive shaft assembly according to claim 9 wherein said connecting means comprises an elastic member which connects said first ends of said first and second shafts in such a manner that said center axes of said first and second shafts are normally held in line with each other, and a relative rotation between said first and second shaft is prevented. 
     
     
       11. A drive shaft assembly according to claim 9 wherein said first unbalancing means comprises first and second mass members which are equal in mass, and said second unbalancing means comprises third and fourth mass members which are equal in mass, said first and second mass members being positioned on a first imaginary circle whose center lies on said center axis of said first shaft, an angle subtended at the center of said first circle by an arc of said first circle extending between the positions of said first and second mass members being substantially a right angle, said third and fourth mass members being positioned on a second imaginary circle whose center lies on said center axis of said second shaft, an angle subtended at the center of said second circle by an arc of said second circle extending between the positions of said third and fourth mass members being substantially a right angle. 
     
     
       12. A drive shaft assembly according to claim 11 wherein said first and third mass members are located on a first imaginary orthogonal plane, and said second and fourth mass members are located on a second imaginary orthogonal plane which intersects said first orthogonal plane substantially at right angles along an intersecting line extending from said second end of said first shaft to said second end of said second shaft, said first orthogonal plane extending between said second and fourth mass members, and said second orthogonal plane extending between said first and third mass members. 
     
     
       13. A drive shaft assembly according to claim 11 wherein said connecting means includes a means which connects said first ends of said first and second shafts with each other in such a manner as to permit a whirling movement of said first end of each of said first and second shafts to a limited extent, and said first and second unbalancing means are positioned in such a manner as to cause said first ends of said first and second shafts to make whirling movements of opposite phase. 
     
     
       14. A drive shaft assembly according to claim 11 wherein said first, second, third and fourth mass members are arranged at equal angular intervals in a circumferential direction.